A self-baking electrode (a so-called Soderberg electrode) is primarily used in the production of ferroalloys in reduction furnaces. Externally the electrode consists of a thin cylindrical casing of iron or steel having a thickness of from 0.2 to 3 mm, depending on the electrode diameter. The casing is constructed by successively welding thin iron or steel pipes, each internally reinforced with ribs and/or sheet metal fins, onto the existing casing at a rate to match that at which the electrode is consumed. An electrode paste is then filled into the pipes from above. The electrode paste often consists of a compound of one or more of anthacite, petroleum coke, graphite, coal pitch, coal tar and wood tar. Further down the electrode, electric current is fed to the electrode via so-called contact shoes. The baking of the electrode paste takes place in a zone adjacent to the contact shoes. A bakes electrode is a good conductor of electricity whereas a non-baked electrode is a poor conductor of electricity. When the electrical current passes through the electrode paste, the paste is heated by the release of resistance heat. The paste softens and melts at a temperature of 50.degree.-100.degree. C., depending on its composition. At 350.degree. C. the baking process starts, and gases and volatile components start escaping. The baking process may continue up to a temperature of about 800.degree. C., at which temperature the last of the volatile substances present in the paste are driven off. The electrode paste has poor conductivity prior to the baking. Therefore, the casing and the internal reinforcement to a large extent have to carry the electric current in the zone immediately below the contact shoes, where the baking process has not yet been completed.
The baking of the electrode paste when using a Soderberg electrode, as described above, is complicated and difficult to control. When the consumption rate of the electrode exceeds that of the baking speed, a so-called green breakage may occur, whereby unbaked electrode paste slides out of the casing and drops into the furnace space. Such an event contaminates material in the furnace, pollutes the environment and is hazardous to personnel operating the furnace.
Another disadvantage with this method of electrode manufacture is that it cannot be automated in a simple manner and that iron or steel sheathed electrodes cannot be used in the manufacture of, for example, silicon metal, in which iron is a harmful impurity. Such silicon metal is used as raw material in the manufacture of silicones, in semiconductor manufacture and for alloying aluminum.
One object of the present invention is to provide a solution to the above-mentioned problems and other problems associated therewith.